Field of the Invention
The invention generally relates to wireless communications, and more particularly, to reducing the packet transmission delay at the user's end, by segmenting and/or concatenating Radio Link Control (RLC) Service Data Units (SDUs) into RLC Packet Data Units (PDUs) in advance.
Description of the Related Art
With growing demand for ubiquitous computing and networking, various wireless technologies have been developed, including the second generation (2G) cellular technology, such as the General Packet Radio Service (GPRS) technology and the Enhanced Data rates for Global Evolution (EDGE) technology; the third generation (3G) cellular technology, such as the Wideband Code Division Multiple Access (WCDMA) technology and the High Speed Packet Access (HSPA) technology; and the fourth generation (4G) cellular technology, such as the Long Term Evolution (LTE) technology and the LTE-Advanced (LTE-A) technology.
For a typical communication environment, a Transmission Control Protocol (TCP) connection may be established from a User Equipment (UE) to a server on the Internet via a cellular network. However, although the data rate over the air interface provided by the cellular network increases substantially along with the evolving wireless technologies, the throughput of the TCP connection over the air interface remains limited by the packet transmission delay (i.e., the Round Trip Time (RTT)) between the UE and the server due to the fact that the TCP throughput is inversely proportional to the packet transmission delay. In other words, when the packet transmission delay is bounded to a certain level, the TCP throughput cannot be increased any further regardless of the actual radio bandwidth available. Specifically, the relation between the TCP throughput and the packet transmission delay can be described with the formula:
      TCP_throughput    ≤          RWIN      RTT        ,wherein RWIN refers to the TCP Receive Window size which is normally determined only by the server and the UE has no control over it.
Since many applications use TCP as the protocol for communication controls and most TCP applications do not apply a large TCP Receive Window size, the TCP throughput is directly affected by the packet transmission delay. FIG. 1 is an exemplary graph illustrating the relation between the TCP throughput and the packet transmission delay for a TCP connection with a fixed RWIN of 64 KB which is established through the HSPA technology. As shown in FIG. 1, the TCP throughput can reach 40 Mbps when the RTT is 12.5 milliseconds long, while the TCP throughput is limited to 22.5 Mbps when the RTT is 25 milliseconds long.
Therefore, it is desirable to reduce the packet transmission delay for improving the throughputs of TCP applications.